In order to protect the integrity of pipelines and flowlines from internal corrosion, corrosion inhibitors are injected. Corrosion inhibitors include any chemical component that, when present in small quantities, produces a reduction in the metal loss of a structure due to corrosion. Corrosion inhibitors are generally organic molecules that accumulate at the metal/solution interface to impede the interaction of water and corrosive components with the metal surface.
Currently, corrosion inhibitors are added to pipelines and flowlines in a liquid mixture. The mixture is composed of several components including: an active component; a solvent, which is used to improve the physical characteristics, such as viscosity, free protection, etc.; a co-solvent, which is used to achieve product stability; a surfactant, which is used to control dispersibility of the chemical in the fluid; and specialty chemicals, such as a demulsifying agent, an antifoaming agent, etc.
Corrosion inhibitors are introduced to the pipelines and flowlines in one of two methods: continuous injection or batch flow. In a continuous application, the inhibitor is continuously injected in small dosages into the pipeline/flowline Inhibitors are typically stored in tanks or vessels at the inlet of the pipeline and utilize a pump to meter and inject the chemical inhibitor.
In batch flow, the inhibitor chemical is delivered by a slug of a large volume of the chemical pushed through the line. Batches can be accomplished with the assistance of pigs. Fluid can either be pushed in front of a pig or transported between two pigs. These batches need to occur at a pre-determined frequency in order to maintain a sufficient amount of chemical at the pipe/fluid interface. Frequency is determined based on: the liquid entry into a pipe, the liquid holdup in the pipe, the size of the slug catcher; the impact of the slug on facilities; the slug size and pipeline inventory; and the amount of debris found in the pig receiver.
A batch flow operation requires the pipeline to be pigged. Pigging can be challenging due to the operational conditions of the pipeline or flowline. Pigging challenges include but are not limited to: the existence of a high flow rate; the existence of a low flow rate; the lack of a pig launcher; the lack of a pig receiver; the existence of a multi-diameter pipeline; an acid and/or gas environment; the existence of barred tees; and the existence of an unpiggable wye joint.
If the batch is not run at the required frequency, the pipeline is at risk for an under dosage of chemicals. The frequency of dosage is also challenging, since it is difficult to account for changing conditions of the pipeline or flowline with age. Moreover, the increase in solids (e.g. sand, wax) will reduce the effectiveness of inhibitors.
The use of liquid corrosion inhibitors requires tanks and facilities to ensure that the pipeline is constantly supplied with the required volume of chemical corrosion inhibitor. The tanks must be maintained and kept full in order to maintain availability of the chemical. Maintaining chemicals at the inlet facility can be challenging at remote locations and offshore locations. Additionally, the injection pump is critical to the functionality of the inhibitor process. Any disruption to injection will lead to a decrease in the inhibitor's effectiveness. In order to be cost effective, continuous injection quantities employed often do not significantly exceed the minimum required in order to maintain protection, while the timing of batch inhibitors is designed to maintain the minimum dosage required. Therefore, any disruption to the injection due to equipment malfunction or chemical availability can lead to risk of corrosion.
Furthermore, as oil and gas operations expand to more remote locations, such as the arctic, delivery of liquid inhibitor can be very challenging. A supply may only be delivered once or twice a year. Therefore, large quantities that are easy to ship and store are required. Several components of the liquid inhibitor can pose health and safety challenges. For example, most liquid inhibitors are based on a methanol solvent, making them highly flammable. Additionally, the handling, transportation, and storage of these chemicals can pose risks to site personnel. An inhibitor in a solid form would be easier to handle, store, and manage at these locations.
Additionally, liquid inhibitors are limited to applications having fluid flows. Pipeline and flowlines with bathymetry that include dead-legs pose additional risks for corrosion when not supplied with the appropriate concentration of liquid corrosion inhibitor.
As such, there is a desire for an alternative solution for pipeline and flowline corrosion inhibition that addresses the aforementioned problems.